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82                    Whitworth Compressed Steel.

would otherwise be wasted, the valves being reversed reguh
whenever the bricks acquire too much heat.

The furnace is first charged with pig iron, and when thii
melted, heated  wrought  iron and  steel  scraps  are  added
degrees (these three in nearly equal proportions).    When all
thoroughly mixed  a  little  piece  of cast  iron, in the form
spiegeleisen, is added, together with a very little manganese.

Experience, the principal guide for this mixture, is again call
into play immediately before completion of the operation, t
foreman trying small samples taken from the furnace and cool
in water, by breaking them and examining the fracture. If sat
factory, the steel is now poured into ladles by tapping at r.

As soon as the metal ceases to flow easily it is known tr,
there is only slag left.    The ladle is then removed, and the si
,*                         allowed to run to the ground or into moulds.

1                              The Landore-Siemens process, also the patent of Sir 1

t|                         Siemens, differs in the fact that iron ore is used direct   On beii

|ij                         first reduced and the slag got rid of, it forms spongy balls ,

tf                         malleable iron,  which are then dissolved in molten  pig  iro

,|1                         spiegeleisen being added as before.    It often receives the nan

l\,                         of the * pig and ore ' process.

n                              In the Siemens process the ore and flux are mixed dire*

with the pig; more slag is therefore produced.

Steel Castings made by any of the above methods mu,
be annealed slowly in a closed  furnace for a week or mon
to prevent cold-shortness.     Honeycombing,  or the presence  <
vacuous spaces in the metal, is the principal trouble, and is parti
, |                          prevented by the addition of silicon, as silico-fenromanganes*

I                          but; is only perfectly got rid of by the Whitworth process, whei

f                          the molten ingot is compressed by powerful hydraulic pressuij

until it is «quite set.    The great advantage of this compressioil
which amounts to from six to twenty tons per square inch, I
'shewn by the fact that the ingot is made to contract as mud
f as one-and-a-half inches per foot of length.    The mould consist
' of a steel cylinder, lined with refractory material, and so con
' strutted that when placed under an hydraulic press, the gasei
may escape through the sides of the mould.   (See App. //.,/, 790.1
1    We may always expect highly carbonised steel to be deficien!